The present invention relates generally to emitter devices utilized in ultra-high density memory storage systems, and more particularly, the present invention relates to an improved solid state emitter that optimizes electron emission in a central location to improve focusing accuracy.
Memory storage systems have made tremendous advancements over the years from the first use of magnetic tape to magnetic hard drives and now optical drives as well as sophisticated fast memory such as S-RAM and D-RAM. A more recent development has utilized field emission electron emitters within an ultra-high density storage device. The field emission electron emitters have typically been fabricated in tip-geometry that emit beams of electrons from the sharp points at the end of the tips. Electron beams are utilized to read or write to a storage medium that is located proximate the field emitters. An array of field emitters may match the array of storage areas within the storage medium or a smaller array of field emitters may be moved relative to the storage medium to access the storage locations on the storage medium.
An example of an ultra-high density storage device utilizing field emitter technology is disclosed in U.S. Pat. No. 5,557,596. Each field emitter typically generates an electron beam current bound by a storage area to generate a signal current. Each storage area can be in one of a few different states, and are most typically in a binary state of either 1 or 0 represented by a high bit or a low bit. The magnitude of the signal current generated by the beam current impinging on the storage area depends on the state of the storage area. Thus, the information stored in the area can be read by measuring the magnitude of the signal current.
The electron beam may also be utilized to write information into the storage area. The power of each electron beam can be increased to change the state of the storage area on which it impinges. By changing the state of the storage area, a bit of information is stored or erased in the storage area, depending upon the beam strength.
The speed and accuracy of information stored, retrieved, and accessed greatly depend upon the efficiency of the field emitters. Further, the manufacturing steps necessary to produce and fabricate field tip emitters is extremely complex. Furthermore, since the storage medium is spaced apart from the field emitters utilized to read or write the information thereof, it is necessary to place those elements within a protective casing under high-vacuum; on the order of 10−7 Torr or less, in order to protect the delicate surfaces of both the emitter tips and the memory array from environmental effects. High-vacuums are expensive and difficult to achieve.
Further, in planar electron emitter technology, when a uniform semiconductor layer is applied to the emitter electrode, electron emission tends to take place at the edge of an emitter because of field concentration due to extractor electrode geometry. This is not desired due to significant curvature of electric field lines in that region which causes the beam to become divergent rather than primarily collimated. It is advantageous to have emission occur primarily in the center of an emitter where the extracting field lines are primarily straight.
What is needed in the field emission electron emitter technology area is a field emission electron emitter that provides a higher efficiency than the prior art, that can be made more consistently at a lower cost than the prior art, that is more immune to environmental effects as well as the need for high vacuum environments typically required in the prior art, and that has a greater emission efficiency rate about the center region in planar electron emitter devices over that of the prior art.